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Subject[PATCH] Xen: Fix retry calls into PRIVCMD_MMAPBATCH*.
Date
From: Andres Lagar-Cavilla <andres@lagarcavilla.org>

When a foreign mapper attempts to map guest frames that are paged out,
the mapper receives an ENOENT response and will have to try again
while a helper process pages the target frame back in.

Gating checks on PRIVCMD_MMAPBATCH* ioctl args were preventing retries
of mapping calls.

V2: Fixed autotranslated physmap mode breakage introduced by V1.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
---
drivers/xen/privcmd.c | 41 +++++++++++++++++++++++++++++++++++------
1 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index f8e5dd7..6ebdf98 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -43,9 +43,12 @@ MODULE_LICENSE("GPL");

#define PRIV_VMA_LOCKED ((void *)1)

-#ifndef HAVE_ARCH_PRIVCMD_MMAP
static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma);
-#endif
+
+static int privcmd_enforce_singleshot_mapping_granular(
+ struct vm_area_struct *vma,
+ unsigned long addr,
+ unsigned long nr_pages);

static long privcmd_ioctl_hypercall(void __user *udata)
{
@@ -422,14 +425,15 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
vma = find_vma(mm, m.addr);
if (!vma ||
vma->vm_ops != &privcmd_vm_ops ||
- (m.addr != vma->vm_start) ||
- ((m.addr + (nr_pages << PAGE_SHIFT)) != vma->vm_end) ||
- !privcmd_enforce_singleshot_mapping(vma)) {
+ (m.addr < vma->vm_start) ||
+ ((m.addr + (nr_pages << PAGE_SHIFT)) > vma->vm_end) ||
+ !privcmd_enforce_singleshot_mapping_granular(vma, m.addr, nr_pages)) {
up_write(&mm->mmap_sem);
ret = -EINVAL;
goto out;
}
- if (xen_feature(XENFEAT_auto_translated_physmap)) {
+ if (xen_feature(XENFEAT_auto_translated_physmap) &&
+ privcmd_enforce_singleshot_mapping(vma)) {
ret = alloc_empty_pages(vma, m.num);
if (ret < 0) {
up_write(&mm->mmap_sem);
@@ -540,11 +544,36 @@ static int privcmd_mmap(struct file *file, struct vm_area_struct *vma)
return 0;
}

+/*
+ * For Asserting on a whole VMA. This is used by the legacy PRIVCMD_MMAP
+ * call and autotranslated physmap mode to allocate the ballooned pages that
+ * back a mapping only once.
+ */
static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma)
{
return !cmpxchg(&vma->vm_private_data, NULL, PRIV_VMA_LOCKED);
}

+/*
+ * For MMAPBATCH*. This allows asserting the singleshot mapping
+ * on a per pfn/pte basis. Mapping calls that fail with ENOENT
+ * can be then retried until success.
+ */
+static int enforce_singleshot_mapping_fn(pte_t *pte, struct page *pmd_page,
+ unsigned long addr, void *data)
+{
+ return pte_none(*pte) ? 0 : -EBUSY;
+}
+
+static int privcmd_enforce_singleshot_mapping_granular(
+ struct vm_area_struct *vma,
+ unsigned long addr,
+ unsigned long nr_pages)
+{
+ return apply_to_page_range(vma->vm_mm, addr, nr_pages << PAGE_SHIFT,
+ enforce_singleshot_mapping_fn, NULL) == 0;
+}
+
const struct file_operations xen_privcmd_fops = {
.owner = THIS_MODULE,
.unlocked_ioctl = privcmd_ioctl,
--
1.7.1


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